Illumination systems configured to produce a train of light pulses that are repeated at high frequency are used as stroboscopic, fast photography lamps for studying ultrafast processes in physics, chemistry, and biology and for light sources in time of flight (TOF) cameras, conventionally referred to as TOF three dimensional (3D) cameras, that provide distance measurements to features in a scene that they image.
Time of flight (TOF) three-dimensional (3D) cameras determine distances to features in a scene by acquiring an image, conventionally referred to as a “range image”, of the scene that can be processed to determine how long it takes light to travel from the camera to the features and back to the camera. The round trip flight times of the light to, and back from the features, and the speed of light are used to determine the distances to the imaged features.
To acquire a suitable range image that can be processed to determine the times of flight, a light source transmits a train of short duration pulses of light to illuminate the scene. Following a predetermined delay after transmittal of each light pulse in the light pulse train, the camera is shuttered open for a short exposure period. Light from the light pulse that is reflected by features in the scene, and that reaches the camera during the exposure period, is imaged by the camera on pixels of the camera's photosensor. An amount of light from all the light pulses in the train that is registered by a given pixel is used to determine a round trip time of flight for light, to and back from, a feature imaged on the given pixel, and therefrom a distance to the feature.
Light pulses in a light pulse train that are transmitted by a light source to illuminate a scene imaged by a TOF 3D camera and exposure periods of the TOF 3D camera may have durations of a few nanoseconds and repetition frequencies greater than a megahertz (MHz). Furthermore, amounts of light that features in the scene reflect from the transmitted light pulses are generally limited. As a result, reflected light available from a feature imaged on a pixel may not be sufficient to determine a distance to the feature having an acceptable signal to noise ratio (SNR).
Compensating for factors that limit light available for acquiring an acceptable range image by increasing light intensity provided by the light source is generally both technically and cost-wise challenging. Cost considerations and heat dissipation requirements for maintaining the light source, and camera, at an acceptable operating temperature usually limit intensity of illumination provided by the light source. The fast switching demands mandated by the high repetition rates that may exceed a megahertz (MHz) of light pulses provided by the light source and a common demand that electronic and optical components of systems have small footprints compound the challenges. A footprint of an electronic component conventionally refers to a size of an area of a circuit board that the component occupies. If a volume that a circuit occupies is a relevant characteristic for consideration, a volume occupied by a component may be understood to be the component's footprint.